I want to start this entry with a huge apology. In the last week, our tech support staff realized that the emails sent to the address below were not reaching my inbox. The problem is now fixed. I have received all the past emails and am working to respond to each. I address one here.
John from Ann Arbor asks:
How does the concept of multiverse fit with the conclusion that time and space were created in the big bang? Does that time and space apply only to our observable universe?
The answer to that question varies depending on the specific multiverse models. In terms of the most prevalent models (those incorporating inflationary cosmology), the answer requires a bit of background. Most people typically envision this scenario when thinking about big bang cosmology:
- Space-time created at the start of the big bang.
- The universe expands, undergoing a period of inflationary expansion in the first fraction of a second. During this inflationary epoch, the universe expands by an enormous factor (25 to 100 orders of magnitude) in a time less than 10-34 seconds.
- The universe cools down, eventually emitting the cosmic microwave background radiation, forming stars and galaxies. Almost 14 billion years later, human beings arrive on planet Earth.
In most inflationary big bang models, the scenario differs in these ways:
- Some pre-existing "space" continually undergoes inflation.
- Our universe begins when inflation stops in some region of this "space"
- If viewed from outside our universe, this bubble region where inflation ceased grows larger as time progresses. The boundary between the inflating region outside the bubble and the non-inflating region inside the bubble represents the big bang. Those inside the bubble cannot see out; those outside the bubble cannot see in.
- The region inside the bubble cools down, eventually emitting the cosmic microwave background radiation, forming stars and galaxies. Almost 14 billion years later, human beings arrive on planet Earth.
In this scenario the big bang no longer represents the creation of space-time. Additionally, it may seem that this multiverse model seriously undermines one of the strongest arguments for God's existence, namely the Kalam cosmological argument. However, as addressed in a previous TNRTB, theBVG theorem developed by Arvind Borde, Alex Vilenkin, and Alan Guth demonstrates that this pre-existing inflating space must have a beginning.
In a stand-alone big bang universe, the creation of space-time relies on the validity of general relativity at the moment of creation. Yet, that is precisely the moment when scientists expect it to break down. The broader BVG theory applies to any inflationary theory capable of explaining this universe. Thus, this research into an inflationary multiverse makes the cosmological argument more robust (at the expense of making it more nuanced).
John goes on to ask:
In that regard, in a recent Message of the Month, you repeatedly said the universe is "flat". What does that mean?
Cosmologists use the term "flat," as opposed to "closed" or "open," to describe the geometry of the spatial dimensions of the universe. By analogy, a piece of paper is flat whereas a ball (closed geometry) and a saddle (open geometry) are both curved. Since astronomers cannot view the universe from the outside, a more observationally useful definition involves how two parallel laser beams travel through space. The distance between the beams as they travel falls into one of three categories: (1) in a closed geometry the beams move closer together; (2) in an open geometry they move farther apart; (3) in a geometrically flat universe, two parallel beams remain separated by the same distance, never intersecting regardless of how far they travel.
If you would like to see a question about the multiverse addressed in this forum, send it to firstname.lastname@example.org.